Studies dealing with the development of embryonic neurons and of organs such as lung, salivary gland, or neural crest will be carried out. Axon initiation, branching, and guidance will be investigated using low density cell culture procedures, time-lapse cinematography, scanning and transmission electron microscopy, and chemical treatments. Growth factors, other that NGF, will be examined under conditions where peripheral nervous system cells grow in the presence of anti NGF sera.. Morphogenesis of induced buds growing from mouse embryonic trachea will be investigated in relation to alterations in cell cycle dynamics, proportion of cells labelling, and changes in extracellular materials in the basal lamina region. Time lapse and scanning EM studies of lungs and salivary glands will be pursued to permit measurements to be made of cell shapes at sites of morphogenetic activity. Finally, scanning electron microscopy of neural crest cell populations will be combined with transplantation between quail and chick embryos in order to study the specificity of pathways in embryos and the degree to which various cell types can respond to foreign pathways.